Nowadays, arc welding robots each produced by attaching an arc welding torch to an end of a six-axis vertical multijoint robot are heavily used in many industrial fields. This six-axis vertical multijoint robot has a turning base (a first basic axis) adapted to turn around a vertical axis on a base stand, a lower arm (a second basic axis) attached to the turning base and adapted to frontwardly and rearwardly swing, an upper arm (a third arm) attached to an end of the lower arm and adapted to upwardly and downwardly swing, and a three-degree-of-freedom wrist portion (first to third wrist axes) attached to an end of the upper arm. In a case where the arc welding torch is attached to an end of the wrist portion, the arc welding torch can take a given attitude at a given position, so that arc welding can be freely performed.
FIG. 8 is a side view of a conventional arc welding robot.
In the figure, reference numeral 3 designates a lower arm, which is pivotally supported by a turning base (not shown) and frontwardly and rearwardly swings. Reference numeral 4 denotes an upper arm that is supported rotatably and pivotally around a U-axis (which is an axis perpendicular to a paper surface) at an end of the lower arm 3 and that swings upwardly and downwardly. Reference numeral 5 designates a wrist portion attached to an end of the upper arm.
The wrist portion 5 comprises a body 6 that rotates around an R-axis extending in the direction of length of the upper arm, a swinging element 7 that is pivotally supported at an end of the body 6 and that swings around a B-axis (which is an axis perpendicular to the paper surface) perpendicular to the R-axis, and a rotating element 8 that is provided at an end of the swinging element 7 and that rotates around a T-axis perpendicular to the B-axis.
Reference numeral 9 designates a welding torch fixed to the rotating portion 8 through a torch clamp 10. Reference numeral 11 denotes a wire feeding unit that is fixed onto the upper arm 2 and that draws out a welding wire from a wire storage unit (for example, a wire reel (not shown)) and pushes out the welding wire to the welding torch 9. Reference numeral 12 designates a conduit cable that connects the welding torch 9 and the wire feeding unit 11. The conduit cable 12 is produced by bundling a welding supply cable and a shielding gas supply hose around a protective tube for feeding the welding wire to the welding torch 9.
However, the conventional arc welding robot has a problem that when the swinging element 7 is caused swing around the B-axis so that the welding torch 9 is made to swing upwardly and downwardly with respect to the upper arm 4, the conduit cable 12 bends to thereby hinder the feeding of the welding wire. Also, the conventional arc welding robot has another problem that when the rotating element 8 is rotated around the T-axis, the conduit cable 12 twines around the wrist portion 5 and the upper arm 4.
To remedy these problems, the conduit cable 12 has been caused to extend over the upper arm 4 in such a way as to form a large arch thereover, as shown in FIG. 7, so that a motion of the welding torch 9 is absorbed by deformation of the arch. However, the conduit cable 12, which has formed a large arch, causes interference with a work and a peripheral device, so that the arch cannot needlessly be enlarged. Thus, complete solution of the problems has not been achieved.